1. Field of the Invention
This invention relates to the field of information networks, and more particularly relates to switching matrices used in routing information through such information networks.
2. Description of the Related Art
Today's networks carry vast amounts of information. High bandwidth applications supported by these networks include streaming video, streaming audio, and large aggregations of voice traffic. In the future, these bandwidth demands are certain to increase. Many modern networking topologies thus employ high speed transport of some kind to achieve the performance necessary to support such applications. Moreover, this information must be quickly and efficiently distributed to various destinations without the introduction of errors.
Several solutions for transporting such data streams exist, a number of which employ synchronous techniques (the Synchronous Optical NETwork (SONET) standard). Given that such techniques are synchronous, by their very nature, they require some level of synchronization of data signals to a clock. This is complicated by the fact that local clocks may vary from one system to another. To address this need, clock recovery circuits are employed within receivers in such systems to establish synchronization between a locally generated clock and the timing of a data stream within a received data signal. The incoming data stream is synchronized to the local clock by recovering the data stream's clock, which can then be used to control recovery of the data. A phase-locked loop (PLL) circuit is often used to provide such clock recovery.
As noted, the incoming data stream in synchronous systems is often not actually synchronous (i.e., having the same frequency and phase) with the local clock. Typically, the data stream's “clock” and the local clock will either be slightly out of phase (referred to as mesosynchronous or mesochronous, meaning that the two signals corresponding significant instants occur at the same average rate (i.e., that their frequencies are, on average, the same)), or slightly out of phase and/or slightly off-frequency (referred to as plesiosynchronous).
The need for synchronous signals mandates systems that are capable of accepting mesochronous datastreams (mesochronous with each other and with the system clock of the receiving system). There is therefore the need to be able to re-time these signals to the system clock of the receiving system, and often to one another. Additionally, it is desirable to provide the ability to tolerate clock failures (e.g., inaccuracy or loss of clock signal), without generating bit errors in the data stream.